Spectrometers are used to analyse samples to identify their properties. A spectrometer usually includes a source of radiation which is used to irradiate a sample and a receiver for receiving radiation either reflected from or transmitted by the sample. The receiver signal is analysed to produce a spectrum which then provides information relating to the sample.
There is a need in spectrometry to make accurate measurements of specular reflectance of a sample over a substantial range of angles and over a wide range of wavelengths, which typically can extend from the ultraviolet (UV) through to the near infrared (NIR). There is an absence of suitable reflectance standards which means that the reflectance of samples has to be measured directly without reference to a standard reflector. Currently there is a lack of suitable equipment available at a reasonable price that can measure reflectance over a significant range of angles and is sufficiently small and compact to be incorporated into modern spectrometers.
Reflectance measurements are usually made using accessories which can be removably coupled to a spectrometer. One known accessory design operates on the basic principle of providing two alternative paths for the light beam in the instrument sample compartment. One path is a sample path in which the beam reflects off the sample and is returned to the spectrometer detector. The other path is a background path in which the beam is directed to the detector and does not reflect off the sample. The ratio of the detected signals is a measure of the sample reflectivity, but its accuracy is dependent upon whether there are differences in the beam transmission energy on the two paths ignoring the effect of the sample itself. Since optical components do not reflect or transmit perfectly, great care is needed to match the performance of the components in the two configurations and the optical path is arranged so that switch-over between paths can be made by reversing two mirrors so that in each configuration the beam is reflected at an identical angle albeit reversed because of the presence or absence of the reflecting sample.
Also known accessories usually make use of the detector of the instrument with which they are used and this can lead to difficulties in providing an arrangement of optical components which will permit reflectance measurements over a wide range of angle of incidence of the beam on the sample.
Another known problem is that of beam and/or detector inhomogeneity. If both are non-uniform the output of the detector changes when the mirror angles are reversed and some form of beam homogenisation is required.
The present invention is concerned with an assembly of components which can be provided as a spectrometer accessory and which is designed to alleviate the problems referred to.
According to one aspect of the present invention there is provided an assembly of components for use with a spectrometer to enable reflectance measurements to be made on a sample, said assembly comprising a sample location, optical elements for directing analysing radiation to said sample location and a detector for receiving radiation reflected from the sample, at least one of the optical elements including a mirror which is rotatable and translatable to enable radiation to be incident on the sample over a range of angles. The sample location may be arranged so that in use the sample is generally horizontal to facilitate sample placement. The optical elements may include a path length compensator. The path length compensator may comprise a mirror which can move linearly and that mirror may comprise a roof mirror.
The detector may be mounted so as to be pivotable relative to the sample. The detector may also be mounted so that it can move linearly relative to the sample. The detector may form part of the detector sub-assembly which includes two detector elements responsive to different wavelengths of radiation. One of the detector elements may have associated therewith an optical scrambler for scrambling the radiation prior to it being incident on the detector element. The scrambler may be a light pipe.
The sample location may be fixed.
The optical elements may be located in a housing and the assembly can take the form of an accessory for a spectrometer. The sample location may be located on the upper surface of the housing. The housing may have an aperture in its upper wall through which the radiation can pass to the sample location.
Another aspect of the invention provides an accessory for use with a spectrometer to enable reflectance measurements to be made on a sample, said accessory comprising a housing providing a sample location, optical elements disposed in said housing for directing analysing radiation to said sample location and a detector for receiving radiation reflected from the sample, wherein the sample location is provided on an upper surface of the housing. The upper wall of the housing may include an aperture through which the radiation can pass to the sample location. The upper wall may include a shutter for opening and closing the aperture.
The accessory may be locatable in the spectrometer in a position normally occupied by the detector of the spectrometer when it is operating without the accessory.
A further aspect of the invention provides an assembly of components for use with a spectrometer to enable reflectance measurements to be made on a sample comprising a sample location, optical elements for directing analysing radiation to said sample location and a detector for receiving radiation reflected from said sample, wherein an optical scrambler in the form of a light pipe is associated with the detector, said radiation passing through the light pipe prior to the detector in order to minimise the effect of inhomogeneities in the detector.
A further aspect of the invention provides an assembly of components for use with a spectrometer to enable reflectance measurements to be made on the sample, said assembly comprising a sample location, a first reflector for receiving analysing radiation propagating generally horizontally and for reflecting the radiation at least partially upwardly to a second reflector, a third reflector for receiving radiation from the second reflector and for directing the radiation along a generally horizontal path which is horizontally displaced relative to that of the incoming radiation, a fourth reflector for directing the radiation towards the sample location and a detector for receiving radiation reflected from the sample. The direction of radiation propagating from the third reflector may be generally opposite to that of the incoming radiation. The third reflector may be a roof mirror. The third reflector can be movable linearly so that it can act as a path length compensator.
The invention will be described now by way of example only, with particular reference to the accompanying drawings.